In lock-protected compressed air braking systems, i.e. anti-lock braking systems, of wheeled vehicles such as motor vehicles and rail vehicles, a valve unit for pressure modulation is provided in each brake line leading from a brake valve to the wheel brake cylinders. This valve unit has an inlet valve and an outlet valve. By means of the inlet valve, a brake pressure output connected to a portion of a brake line which leads to at least one wheel brake cylinder, may be alternately connected to or shut off from a brake pressure input connected to a portion of the brake line which comes from the brake valve. The brake pressure output may be alternately connected to or shut off from a purge output using the outlet valve, wherein the purge output usually leads via a check valve and/or a screen into the ambient air.
Because of large volume flows to be switched, and correspondingly large flow cross-sections to be opened and closed, the inlet valve and the outlet valve are normally configured as pneumatically actuatable diaphragm valves which can be activated via a respective precontrol valve configured as 3/2-way solenoid valve. A diaphragm valve has a largely circular, disc-like flexible membrane which is clamped at its edge in a valve housing. A central, round valve seat of a cylindrical inner flow channel, with an annular outer flow channel arranged concentrically thereto, is arranged on the axial inside of the diaphragm on which the flow channels are arranged which are connected to the compressed air input and compressed air outputs. On the axially opposite outside of the diaphragm, a control chamber is arranged which can be loaded by the assigned precontrol valve alternately with a high control pressure, usually taken from the brake pressure input, or with a low control pressure (ambient pressure), usually taken from the purge output. When the control chamber is loaded with the high control pressure, the diaphragm is pressed against the valve seat, whereby the inner flow channel is isolated from the outer flow channel, which corresponds to the closed state of the diaphragm valve concerned. When the control chamber is loaded with the low control pressure, the diaphragm which due to its shape normally lies automatically on the valve seat, is lifted away from the valve seat by the brake pressure predominating in the flow channels and moved in the direction of the control chamber, whereby the inner flow channel is connected to the outer flow channel, which corresponds to the open state of the diaphragm valve concerned.
Such a valve unit has the switch functions “build up pressure”, “maintain pressure”, and “reduce pressure”. In the “build up pressure” switch function of the valve unit, the inlet valve is opened and the outlet valve is closed, so that the brake pressure introduced via the brake valve at the brake pressure input is conducted unchanged to the brake pressure output and to at least one wheel brake cylinder connected thereto. Since the “build up pressure” switch function corresponds to the rest state of the valve unit, the precontrol valve of the inlet valve, when its magnetic coil is not powered, connects the control chamber of the inlet valve to a control line carrying the low control pressure. Similarly, the precontrol valve of the outlet valve, when its magnetic coil is not powered, connects the control chamber of the outlet valve to a control line carrying the high control pressure.
In the “maintain pressure” switch function of the valve unit, the inlet valve and the outlet valve are closed so that the brake pressure, present at the brake pressure output and at the at least one wheel brake cylinder connected thereto, is held constant. To set this switch function, only the precontrol valve of the inlet valve is switched by powering its magnetic coil, and hence the control chamber of the inlet valve is loaded with the high control pressure.
In the “reduce pressure” switch function of the valve unit, the inlet valve is closed and the outlet valve opened so that the brake pressure output and the at least one wheel brake cylinder connected thereto are purged. To set this switch function, both precontrol valves are switched by powering their magnetic coils, and hence the control chamber of the inlet valve is loaded with the high control pressure and the control chamber of the outlet valve is loaded with the low control pressure.
The “maintain pressure” and “reduce pressure” switch functions of the valve unit are antilock functions with which a braking-induced locking of the at least one assigned wheel is avoided. These switch functions are controlled by a corresponding actuation of the precontrol valves by a control unit of the anti-lock system, in which the signals from the wheel speed sensors are analyzed to detect an impending or existing locking of the braked wheels.
With regard to the geometric arrangement of the compressed air inputs and compressed air outputs, the inlet valves and outlet valves configured as diaphragm valves, and the precontrol valves configured as solenoid valves, in a valve housing, various embodiments of such valve units are known.
Thus for example publications DE 22 24 274 C3, DE 34 08 123 A1, DE 38 25 549 A1, DE 40 05 608 A1 and DE 40 08 095 A1 describe various embodiments of valve units in which the diaphragm planes of the inlet valve and outlet valve are oriented perpendicular or parallel to each other. The precontrol valves configured as 3/2-way valves in these valve units are arranged either with different orientation of the actuation axes close to the assigned diaphragm valve, or parallel and radially adjacent to each other in different regions of the respective valve housing.
Because of the arrangement of the compressed air inputs and compressed air outputs, the inlet valves and the outlet valves, and the precontrol valves, in the above-mentioned valve units a multipiece design and complex machining of the respective valve housing are required. In particular, the respective arrangement of the diaphragms of the inlet valve and outlet valve in different diaphragm planes requires multiple re-clamping of the housing parts for machining of the valve seats and the channel edges or chamber edges between which the diaphragms are clamped. To reduce the production complexity, therefore, valve units have already been proposed in which the diaphragm valves are arranged with parallel actuation axes and diaphragms arranged in a common diaphragm plane, largely corresponding to a division plane between two housing parts.
Such a valve unit is described for example in DE 25 17 571 A1. In this known valve unit, an elongate valve housing is divided by a division plane that is horizontal in the installation position into a housing lower part and a housing upper part. The brake pressure input and the purge output are positioned largely axially opposite in the longitudinal direction with horizontal orientation, and the brake pressure output, also with horizontal orientation, is arranged largely centrally at right angles thereto in the housing lower part. The diaphragm valves are arranged in the housing lower part between the brake pressure input and the purge output, with parallel actuation axes and diaphragms arranged in a common diaphragm plane, largely corresponding to the division plane, being clamped between the housing lower part and the housing upper part, behind each other in the longitudinal direction of the valve housing. The precontrol valve of the inlet valve and the precontrol valve of the outlet valve are each arranged with vertical orientation of their actuation axes and with the same switching directions above the respective assigned diaphragm valve, radially adjacent to each other in the housing upper part, whereby the installation height of the housing upper part and hence the entire valve unit is relatively large.
In a further such valve unit known from EP 0 498 584 B1, the valve housing is divided by a division plane which is vertical in the installation position into an input housing and an output housing. The brake pressure input is arranged with horizontal orientation at the top in the input housing. The brake pressure output is arranged, with horizontal orientation, largely axially opposite the brake pressure input in the output housing, whereas the purge output is arranged oriented vertically downward in the output housing. The diaphragm valves are arranged above each other in the output housing between the brake pressure output and the purge output, with parallel actuation axes and diaphragms arranged in a common diaphragm plane, largely corresponding to the division plane, being clamped between the output housing and the input housing. The precontrol valve of the inlet valve and the precontrol valve of the outlet valve are each arranged with horizontal orientation of their actuation axes and opposite switching directions, approximately at right angles to the compressed air inputs and compressed air outputs and parallel to the division plane, radially adjacent to each other in the input housing. The magnetic coils of the precontrol valves are arranged in a magnet block which, together with the mechanical components of the solenoid valve used, is arranged between a housing upper part and a housing lower part of the input housing. For sealing, seals or sealing rings are arranged between firstly the magnet block, valve blocks and valve seats of the solenoid valves, and secondly the housing upper part and housing lower part of the input housing. To fix the housing upper part and housing lower part to the magnet block of the solenoid valves, and also to clamp the diaphragms of the diaphragm valves, the housing upper part and the housing lower part of the input housing are each bolted to the output housing. This known valve unit thus consists of many components which are relatively difficult to fit. Production and assembly of this known valve unit are therefore relative complex and costly.
Finally, DE 10 2008 028 439 B3 describes a valve unit in which an elongate valve housing is divided by division planes that are largely horizontal in the installation position, into a housing lower part, a housing upper part and an intermediate plate arranged in-between. The brake pressure input, the brake pressure output and the purge output are each arranged with horizontal orientation in the housing lower part. The diaphragm valves are arranged in the housing lower part with parallel actuation axes and diaphragms arranged in a common diaphragm plane, largely corresponding to the division plane between the housing lower part and the intermediate plate, being clamped between the housing lower part and the longitudinal intermediate plate, behind each other in the longitudinal direction. The precontrol valve of the inlet valve and the precontrol valve of the outlet valve are each arranged with vertical orientation of their actuation axes and with the same switching directions above the respective assigned diaphragm valve, radially adjacent to each other in the housing upper part, whereby the installation height of the housing upper part and hence the entire valve unit is relatively large. The intermediate plate is bolted to the housing lower part. The housing upper part is bolted via an outer cover to the intermediate plate or the housing lower part. Seals are arranged in the division plane between the housing upper part and intermediate plate. This valve unit too consists of many components, which are however relatively simple to install from above. Nonetheless, the production and assembly of this known valve unit are also relatively costly.